gto observing program and target list jeffrey linsky and cool star mafia cos team meeting space...
DESCRIPTION
Brown dwarf observing program: Testing structural scenarios Question: Are young brown dwarfs with disks low mass versions of CTTSs? Question: Is the high T gas heated by (MHD) accretion from disks (or close secondaries). Question: Is the H 2 emission Lyα fluorescence? Question: Are the older brown dwarfs without disks low mass versions of active M dwarfs with flare-event (transient) heating? Question: How does the absence of H core burning (due to low mass and/or age) change the outer atmosphere structure and heating from that seen in M dwarfs?TRANSCRIPT
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GTO Observing Program and Target List
Jeffrey Linsky and Cool Star Mafia
COS Team meetingSpace Telescope Science
Institute26 October 2007
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Cool Stars COS Observing Program Program Targets Orbits
Brown dwarfs 6* 29*
Metal deficient chromospheres 1 2
Alien dwarfs 1 8
Pre-main sequence stars 4 16
Solar mass stars: cradle to grave 3 5
Transiting Planets 1 20
Total number of orbits 16 80
*Deeper exposures for two of the brown dwarf targets included in # of orbits.
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Brown dwarf observing program: Testing structural scenarios
• Question: Are young brown dwarfs with disks low mass versions of CTTSs?
• Question: Is the high T gas heated by (MHD) accretion from disks (or close secondaries).
• Question: Is the H2 emission Lyα fluorescence?• Question: Are the older brown dwarfs without disks low
mass versions of active M dwarfs with flare-event (transient) heating?
• Question: How does the absence of H core burning (due to low mass and/or age) change the outer atmosphere structure and heating from that seen in M dwarfs?
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Ultraviolet spectra of L and T dwarfs (collisionally excited and fluorescent lines)
• 2MASSW J1207334-393254 (0.03Msun, 70 pc) is the closest L dwarf with a disk.
• STIS G140L 5.0ks obs by Gizis et al. 2005). Age ~10 Myr
• Study the chromospheric and fluorescent (H2 and ?) lines for a range of L and T dwarfs of different ages and compare with M dwarfs.
• What is the amount and character of nonradiative heating processes in cool fully convective stars?
• 7 targets. Number of orbits 36.
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Preliminary BD target list
Target (2MASS or other) SpType d(pc) J 1207334-393254 M8bin 59(TYA) 12.98VB10 M8 5.78LHS 1070C L0 7.711507476-162738 L5 7.33 12.821315309-264951 L5 55(TYA) 15.180255035-470050 L8 4.9 13.231237+6526 T6bin? 14 15.4
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Information on 2MASS 1207• Probably in the TW Hya Association with age 6-
10 Myr. Evidence for accretion like TW Hya.• Closest known BD with a disk. Very strong Hα
emission.• Emission lines of C II-IV, O I, and He II detected
in the STIS G140L 5 ks exposure.• Many H2 emission lines seen pumped by Lyα.
Compare with or reconstruct the Lyα emission line to test.
• C IV count rate with COS G130M would be 0.5/sec.
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COS Simulated G140L spectrum of 2MASS1207 (6ks, night)
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COS Simulated G130M and G160M spectra of 2MASS1207
• 6 ks night spectra.• C III, N V, C II, O I, C
IV, and He II fluxes from STIS.
• Fluorescent H2 emission (observed in STIS spectrum) are scaled from TW Hya spectrum.
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Brown dwarf observing program: Proposed plan
• For 2MASS1207 the line fluxes are known, so obtain G130M and G160M exposures and a deep G140L exposure (9 orbits).
• For the other 6 targets first obtain 2 orbit test exposures with G140L (12 orbits).
• Then decide which targets to obtain deeper G140L or G130M and G160M exposures (3 stars, 5 orbits each = 15 orbits).
• Total request 36 orbits.
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Activity in Ancient Metal Deficient Chromospheres
• Question: How are the physical properties and heating mechanisms of chromospheres in very metal deficient giants different from normal metal stars?
• Question: Does extreme age and low metalicity change the cooling channels and lead to pure acoustic (basal heating) without any magnetic heating?
• Proposed by Graham Harper (CASA).• Targets: 2 stars, 2 orbits each, G140L (1230Å setting to
avoid Lyα), FP-SPLIT=2 or 4.• HD 216143: [Fe/H]=-2.3, V=7.82, vrad = -116 km/s (see
simulated spectrum).• HD 6833: [Fe/H]=-1.6, V=6.75.
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Activity in Ancient metal Deficient Chromospheres: A simulated Spectrum• 2 orbit G140L spectrum
of HD 216143.• Collisionally-excited and
fluorescent lines (e.g. OI).• Scaled from α Boo using
COS simulator.• GHRS Mg II spectra
useful.• GHRS G160M 6 ks
spectrum and long IUE SWP-LO spectra show only noise and geocoronal emission.
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Alien Dwarfs: Studying the Arcturus Moving Group
• Background: The Arcturus MG studied by Eggen consists of high velocity stars captured from another galaxy with [Fe/H] = -0.68 (1/5 solar).
• Question: How does metal poverty change the heating, structure, and dynamics of the outer layers of stars?
• Observe fluxes and line widths of C IV, Si IV, O IV, Si II, and He II lines.
• 1 target observed with G140L , G130M, and G160M, 12 orbits total.
• To be analyzed by Alec Brown.
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Alien Dwarfs: Targets and Observing Program
• Target: HD 199288, V=6.5, d=21.6 pc.• Age: 6-7 Gyr.• Brightest known alien G dwarf. • No previous UV spectra of the aliens.• X-ray detections and Ca II flux predict UV emission line
fluxes somewhat below solar minimum values.• Predict G140L C IV 1550Å peak count rates of 0.1
cts/RE/s and S/N=30 in 5 ks (line fluxes in 1.5 orbits).• Predict G160M C IV 1550Å peak count rates of 0.02
cts/RE/s and S/N=15 in 12 ks (line widths in 4 orbits).• G130M to measure C II and other line widths (1.5 orbits).
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Evolution of activity of solar mass stars: from the cradle to the grave
• Question: How does chromospheric and coronal activity decline as stars lose angular momentum and magnetic fields with age?
• Important for predicting the atmospheres of young planets that are blasted by strong UV radiation and stellar winds from young stars.
• Measuring fluxes and profiles of emission lines formed at different temperatures needed to predict the ionizing flux and wind from the star.
• Extension of Tom Ayres’ “Sleuthing the Dynamo” project with HST/STIS. Excellent STIS spectra of α Cen (G2 V) and α Boo )(K2 III) available for comparison.
• 4 targets, 10 orbits total.
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Evolution of solar mass stars: simulated COS G130M and G160M spectra
• Top in each panel: β Hydri (G2 IV, 7 Gyr, 8 pc).
• Middle: HD 28344 (Hyades G2 V, 600 Myr, 44 pc).
• Bottom: HII 314 (Pleiades G1 V, 100 Myr, 130 pc).
• Horizontal lines: overlight (100 cts/s/RE), S/N=30, and S/N=10.
• HD 28344 and HII 314 observed with FOS. TTAG mode to look for flares.
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Evolution of solar mass stars: The age (activity) sequence
• The youngest G star: HD 14082B (in β Pic MG, age=10Myr, d=34pc). Simulated spectra of HD 14082B (top), HII 314 (below).
• 10 Myr (HD 14082B)• 100 Myr (HII 314)• 600 Myr (HD 28344)• 5 Gyr (α Cen)• 7 Gyr (β Hyd)
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Accretion flows and winds of PMS stars
• STIS E140M spectrum (2.3ks) of the brightest TTS TW Hya. Face-on disk. 56 pc. mv=11.1
• Evidence for accretion flows in CIV and NV lines and wind absorption in CII and Lyα.
• Need high S/N of several TTS with different inclination angles to determine T range, flow velocities, and column densities of inflows and outflows.
• 4 TTS observed for 4 orbits each. E.g. V4046 Sgr, DF Tau, BP Tau, GG Tau.
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Atmospheres and winds of transiting planets
• Transit of a close-in Jupiter-like planet (Porb≈3 days) around HD 209458 (G0 V).
• Apd/Astar ≈ 1.5% but absorption in Lyα 5±2% and in C II 7.5±3.5%.
• STIS G140L resolution (600 km/s) so absorption width, Doppler shift, and central depth not measured. Also stellar line flux variable.
• Need COS for high S/N and 15 km/s resolution.
• Vidal-Madjar et al. proposed a hydrodynamic escape model for the outflow but mass loss rate very uncertain.
Vidal-Madjar et al. ApJ 604, L69 (2004)and Nature 422, 143 (2003)
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Why observe a transiting planet?• Lifetime and evolution of
“roasters” could be determined by atmospheric loss rate.
• What is chemical composition of the atmospheres?
• What physical processes dominate the mass loss?
• Observations at quadratures (±130 km/s) may show scattered light and/or aurorae.
• Demonstration of COS capabilities: high time resolution, sensitivity, and ability to detect weak features.
• HD 189733b an alternative. 4 orbits of STIS G140Ldata during midtransit.
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Cool Stars COS Observing Program Program Targets Orbits
Brown dwarfs 6* 29*
Metal deficient chromospheres 1 2
Alien dwarfs 1 8
Pre-main sequence stars 4 16
Solar mass stars: cradle to grave 3 5
Transiting Planets 1 20
Total number of orbits 16 80
*Deeper exposures for two of the brown dwarf targets included in # of orbits.
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Supplementary Slides
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Information on VB10
• M8 standard star.• Hα in emission.• X-ray emission detected (Fleming et al.
ApJ 594, 982 (2003)). Quiescent emission log Lx/Lbol = -4.9.
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Information on LHS 1070C
• 2MASS 0024442-270825 data in Cruz et al. (AJ 133, 439 (2007).
• Nearest L0 brown dwarf.
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Information on 2MASS 1507
• Data in Cruz et al (2007)• Nearest L5 brown dwarf
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Information on 2MASS 1315
• See Gizis (ApJ 575, 484 (2002)).• Probable member of the TW Hya
Association.• Very strong Hα emission.• Mass about 0.025 solar.
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Information on 2MASS 0255
• Also DENIS-P J0255-4700.• Data in Cruz et al. (2007)• Nearest known L8 brown dwarf.
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Information on 2MASS 1237
• See Burgasser et al. (AJ 123, 2744 (2002)).
• Very strong Hα emission. LHα/Lbol far above all studied L and T dwarfs.
• Possible Hα velocity shifts suggests a BD binary.
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Advantages of COS for observations of cool stars
• G130M mode (20,000 res. 1132-1469Å) is 10-20 times more sensitive than STIS E140M (40,000 res. 1140-1735Å)
• G160M mode (20,000 res. 1382-1798Å) ~10 times more sensitive than STIS E160M at C IV 1550Å.
• G140L mode (2,500 res. 1105-2378Å) X times more sensitive than STIS G140L at C IV 1550Å.
• 2.5” aperture (no slit loss, good for photometry, include CS emission)
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Disadvantages of COS for observation of cool stars and ISM
• 2.5” aperture means strong Lyα (and O I 1302Å) geocoronal emission 35 cts/s (night) or 200 cts/s (day). In principle, this can be subtracted.
• S/N ≈ 45 with FP-SPLIT.• Cannot separate stellar
from CS emission.• No R=100,000 mode or
long slit spectral imaging or coronography.